Factual error: Celestial navigation can determine one's position on the earth's surface to within about one mile, not precise enough to give the location of a buried treasure. It also requires more than a sextant. It requires tables published in a nautical almanac (which is updated each year), charts on which to plot lines of position, and an accurate chronometer that is set to the precise time at the Prime Meridian (Greenwich Mean Time).
Factual error: When Buck's body is found, his blood is red when it should be brown due to oxidation after how much time has passed.
Chosen answer: This is the very reason my brother and I used to jokingly call the show, "Murder, She Caused." It's amazing she was ever on anyone's guest list for a party, given the likelihood someone would end up deceased. As to your question, most of the time, Jessica Fletcher would have had an air-tight alibi, as she was in a room full of people, or her whereabouts were accounted for when a murder occurred elsewhere. It also seems to me that there were episodes where she, purely with respect to opportunity, could have been a suspect. I believe she even acknowledged that as a logical possibility from time to time, even though she knew, of course, she was not the killer. However, the investigation would obviously rule out the possibility of her involvement, eventually.
Michael Albert